Good point but there are some distinct differences.
First, Bush is not accused of ignoring a threat to our safety while Hastert is accused of ignoring a threat to the safety of children placed under our trust. Even if Bush lied (which he didn't of course) he did for purposes that were intended to protect us. However, if Hastert lied (which he did not of course) the only explanation is he did this to protect his own self and other GOP members at the risk of the well being of children.
The second distinction is that Bush didn't make a call to investigate the so called lies he is accused of while Hastert himself believes a crime may have been committed.
Bush is accused of lying to get us into a major war which gets our men and women killed...you don't call that a threat to their safety? The accusation against Pres. Bush is a much more serious accusation than what's being thrown at Hastert.
By your logic, Bush should step down until he is investigated thoroughly.